Anti-magic zone aint all that on a boss. See the shield only holds for 10kish damage, which sounds like a lot but really its 10k damage over 5 characters, so 2k per character. I guess thats 10k total per character if you use them all, but I think the points are better spent elsewhere. In fact I used my anti magic shield on that mage ho in this instance and it seriously was gone in 1 sec. =(

I think 20% healing for damage is your best bet.

edit: actually you know what I am finding is INVALUABLE as a DK? The frost talent that gives you resist vs all. That + frost stance(obviously only for tank) means AE and DD is dropped about 25%ish percent. Saves a lot of healing for my druid.